1. Field of the Invention
This invention relates generally to bicycle gear changing mechanisms, and more particularly to a bicycle derailleur that has a generally one-piece construction made from molded plastic.
2. Description of the Background Art
Non-encapsulated bicycle derailleurs are exposed to harsh environmental conditions such as road dirt, mud, gravel strikes and salty water. Over time, bicycle use and harsh conditions lead to excessive wear on the derailleur, which then requires replacement. As a derailleur may need to be replaced many times over the useful life of a bicycle, cost becomes an important factor in its construction.
U.S. Pat. No. 4,330,137 discloses a bicycle derailleur that is attached to a bottom bracket of a bicycle instead of being attached to the bicycle seat tube, which is the customary attachment point. The derailleur comprises at least three different linkage members that are pivotally connected to each other and move in relation with each other to position a chain guide. The multiple linkages comprising the derailleur require additional hardware for complete assembly and the unit will need to be painstakingly adjusted when incorporated into a bicycle. The additional materials and increased labor during assembly add to the cost of the derailleur.
U.S. Pat. Nos. 4,199,997 and 4,199,998 both teach a multi-linkage derailleur, where the links must pivot in relation to each other in order to move a chain guide in a direction perpendicular to the bicycle seat post member. The derailleur construction is complex and does not lend itself to a one or two piece construction, thus requiring fine adjustment and increased manufacturing costs.
U.S. Pat. No. 3,890,847 discloses an encapsulated derailleur device which addresses the problem of stretching or breaking the control cable if an operator attempts to shift gears while the bicycle is stationary. The derailleur is quite complex, incorporating a lever, shifting arm, adjusting screws and a flexible spring enclosed within a housing. The great number of parts comprising this portion of the derailleur increases the manufacturing costs.